The invention relates to a motor pump unit for a high-pressure cleaning apparatus having a liquid-cooled electric motor and a pump, wherein the electric motor has a cup-shaped motor housing that is surrounded by a cooling housing with an annular space having an annular space inlet and an annular space outlet formed therebetween, and wherein the pump has a suction inlet connected to the annular space outlet for drawing in liquid and a pressure outlet for discharging liquid, and wherein the liquid to be transported by the pump can be supplied to the annular space inlet.
Motor pump units of this type are known from DE 10 2007 009 394 A1. They are used in high-pressure cleaning apparatuses in which a liquid, preferably water, can be pressurized and then discharged via the pressure outlet. The pressure outlet can have connected to it a high-pressure hose with, for example, a spray lance or a spray nozzle at its free end. This provides the possibility of directing a high-pressure liquid jet towards an object in order, for example, to clean the object.
The pump is driven by means of an electric motor which is cooled by the liquid that is supplied to the pump. To this end, the motor housing is surrounded by a cooling housing shaped in a cylindrical shell configuration, wherein an annular space is formed between the motor housing and the cooling housing which can be supplied with liquid via an annular space inlet. The liquid can flow through the annular space and reach the suction inlet of the pump by way of the annular space outlet, so that it can then be pressurized.
In many instances, the pump is connected to a public water supply network. Within the water supply network, the liquid is subject to a delivery pressure of several bars, for example 3 to 10 bar. As a result, the delivery pressure that exists within the water supply network also exists within the annular space. This in turn causes the motor housing to be exposed to considerable pressure, directed radially inward, from the liquid. The motor housing has to withstand this pressure. However, for manufacturing reasons, it should have as small a wall thickness as possible. There is therefore a risk that the motor housing may be damaged by the liquid pressure prevailing in the annular space if the annular space extends over areas of the motor housing that are not supported inside by the stator of the electric motor. This could be counteracted by having the annular space extend over only a partial area of the shell of the motor housing. This, however, would result in a restricted cooling effect.